1. Field of the Invention
The present invention relates to a solid-state image pickup element and a method of manufacturing the same, and an electronic apparatus. More particularly, the invention relates to a solid-state image pickup element which makes it possible to suppress coloring due to a locus-like noise caused when an image of a moving high-luminance subject is captured and a method of manufacturing the same, and an electronic apparatus using the same.
2. Description of the Related Art
Although many CMOS (Complementary Metal Oxide Semiconductor) image sensors include an electronic shutter function, a rolling shutter (focal-plane shutter) is a basis in the CMOS image sensor. In the rolling shutter, multiple pixels two-dimensionally arranged are successively scanned every pixel row to reset a signal. Therefore, a period of time for an exposure operation is shifted every screen row. As a result, in the case where a subject is moving, or the like, a distortion is generated in a captured image. For example, when a subject extending straight in a vertical direction moving in a transverse direction is photographed, the subject is photographed just as if the subject is inclined.
In order to cope with such a situation, a full-pixel simultaneous electronic shutter for a CMOS high-speed image sensor has been developed. The full-pixel simultaneous electronic shutter is such that an exposure operation is simultaneously started about all the pixels effective in image capturing, and the exposure operation is simultaneously ended, and is called a global shutter (global exposure) as well.
FIG. 1 shows a pixel structure of a CMOS image sensor (solid-state image pickup element) which can carry out a full-pixel simultaneous electronic shutter operation proposed in Japanese Patent Laid-Open No. 2008-103647 (refer to FIG. 3).
The solid-state image pickup element shown in FIG. 1 has a semiconductor region 1 of a first conductivity type (P-type), and a surface buried region 11a of a second conductivity type (N-type) for receiving a light. In this case, the surface buried region 11a of the second conductivity type (N-type) for receiving a light is buried in a part of an upper portion of the semiconductor region 1 in order to receive a light made incident thereto. In addition, an electric charge holding region 12a of the second conductivity type (N+-type) is disposed in a part of the upper portion of the semiconductor region 1, that is, a position laterally located away from the surface buried region 11a for receiving a light. In this case, the electric charge holding region 12a of the second conductivity type (N+-type) holds signal electric charges generated by the surface buried region 11a for receiving a light. In addition, an electric charge reading region 13 of the second conductivity type (N+-type) is disposed in a part of the upper portion of the semiconductor region 1, that is, in a position laterally located away from the electric charge holding region 12a. In this case, the electric charge reading region 13 of the second conductivity type (N+-type) receives the signal electric charges held by the electric charge holding region 12a. It is noted that the electric charge holding region 12a is deeper in potential well than the surface buried region 11a for receiving a light.
In addition, a transfer gate electrode 31 is disposed on an insulating film 2. In this case, with the transfer gate electrode 31, a potential of a first transfer channel formed between the surface buried region 11a for receiving a light and the electric charge holding region 12a is controlled, thereby transferring the signal electric charges from the surface buried region 11a for receiving a light to the electric charge holding region 12a. In addition, a reading gate electrode 32 is disposed on the insulating film 2. In this case, with the reading gate electrode 32, a potential of the second transfer channel formed between the electric charge holding region 12a and the electric charge reading region 13 is controlled, thereby transferring the signal electric charges from the electric charge holding region 12a to the electric reading region 13.
A light blocking film 41 is provided above the electric charge holding region 12a in order to prevent a light from being leaked to the electric charge holding region 12a to add a signal while the signal electric charges are held in the electric charge holding region 12a. 
A photodiode D1 is composed of the surface buried region 11a for receiving a light serving as a cathode region, and the semiconductor substrate 1 serving as an anode region and provided right below the surface buried region 11a for receiving a light. Likewise, an electric charge accumulating diode D2 is composed of the electric charge holding region 12a serving as the cathode region and the semiconductor substrate 1 serving as the anode region and provided right below the electric charge holding region 12a. Also, a P+-type pinning layer 11b is provided so as to overlie the surface buried region 11a for receiving a light, and a P+-type pinning layer 12b is provided so as to overlie the electric charge holding region 12a. 
The photodiode D1 receives a pulse light made incident thereto through an opening portion of the light blocking film 41 in the form of an optical signal, and converts the resulting optical signal into signal electric charges. A high voltage is applied to the transfer gate electrode 31 simultaneously for all pixels, whereby the signal electric charges generated by the surface buried region 11a for receiving a light are perfectly transferred to the electric charge holding region 12a. A high voltage is applied to the reading gate electrode 32, whereby the signal electric charges held in the electric charge holding region 12a are successively transferred to the electric charge reading region 13.
As has been described, in the CMOS image sensors which can carry out the full-pixel simultaneous electronic shutter operation, the electric charge holding region 12a is provided every pixel.
Here, in the case where the light blocking property of the light blocking film 41 is insufficient, when a light is received from a high luminance subject while the signal electric charges are held in the electric charge holding region 12a, a signal is leaked to the electric charge holding region 12a to turn into a noise. In addition, when the subject is moving, a noise is generated so as to have a locus-like shape along which the subject has moved (hereinafter referred to as “a locus-like noise”).
FIG. 2 shows a structure of a CMOS image sensor having the pixel having the structure shown in FIG. 1.
A color filter (not shown) for passing only a light in a wavelength region corresponding to any one of Red (R), Green (G) and Blue (B) is disposed on an upper portion of each of the pixels. In FIG. 2, colors of the color filters of the respective pixels are indicated by characters R, G and B. It is noted that a pixel arrangement of the R, G and B pixels shown in FIG. 2 is an example of a Bayer arrangement. When the high luminance subject moves for such a pixel arrangement of the R, G and B pixels as indicated by a block arrow represented by a heavy solid line, a ratio of an amount of signal electric charges, and an amount of signal electric charges leaked (leaked signal suppression ratio) differs among the R, G and B pixels. In FIG. 2, a black arrow represented by a light solid line indicates a flow of the leaked electric charges, and a black arrow represented by a light dotted line indicates the noise.
Since the leaked signal suppression ratio differs among the R, G and B pixels, a color caused by the locus-like noise generated becomes a color different from that of the subject. With regard to a concrete example, the locus-like noise whose color is seen when a white LED (Light Emitting Diode) light bulbs as the high luminance subject moves is outputted so as not to have a white color, but is outputted so as to have a color like an orange color.
FIG. 3 shows an example of a structure of a CCD (Charge-Couple Device) image sensor corresponding to the structure shown in FIG. 2.
In the CCD image sensor, the electrons generated in a photodiode by photoelectric conversion are transferred simultaneously for all the pixels to a vertical transfer register common either in a longitudinal direction or in a transverse direction to be read out in a line-sequential manner. Therefore, the electric charges generated in a portion, having a high luminance, of the high luminance subject turn into a streak-like noise (smear). In this case, since the electric charges leaked from the R, G and B pixels are mixed in the common vertical transfer register, which of the R, G and B pixels an amount of electric charges are leaked to is not distinguished. Therefore, a problem about the coloring due to the leaked light like the CMOS image sensor is not caused.
Some CCD image sensors are intended to reduce the leaked light. For example, as shown in FIG. 4A, Japanese Patent Laid-Open No. Hei 7-122721 (refer to FIG. 2) proposes a technique such that a thickness X of the gate insulating film 53 formed between an n-type region 51 serving as a photoelectric conversion portion, and a light blocking film 52 is reduced, thereby reducing a quantity of leaked light. As shown in FIG. 4B, as the thickness X of the gate insulating film 53 is reduced, a quantity of leaked light is reduced, and a smear level is also reduced.